The proposed studies are designed to evaluate the potential for transmission of CMV between baboon and human following xenotransplantation. Specific Aim 1 will optimize CMV detection and identification methods, and will use these methods to analyze the spectrum of BCMV isolates which can be found in different animals. These studies will use newly developed RFLP and BCMV-specific PCR methods to selectively identify human CMV (HCMV) and BCMV and to identify strains of BCMV. Specific Aim 2 will seek in vitro evidence that HCMV and BCMV can recombine in co-transfection studies that use HCMV and BCMV with differential molecular markers. Specific Aim 3 will determine the immunologic factors that influence transmission of CMV across species barriers. These studies will focus on serologic and T cell reactivity to BCMV vs. HCMV. Specific Aim 4 will determine whether CMV can cross species barriers in vivo by infecting baboons with HCMV.